Liquid crystal display

ABSTRACT

A liquid crystal display is disclosed. The liquid crystal display includes a liquid crystal display panel including a pixel array and touch sensors, a transparent conductive layer on one substrate of the liquid crystal display panel transmitting display light, a polarizing plate on the transparent conductive layer, a driving voltage supply circuit, and a signal transmitting unit electrically connecting the transparent conductive layer to the driving voltage supply circuit. A portion of the transparent conductive layer is connected to a ground level voltage source. The driving voltage supply circuit generates a driving voltage required to perform light sensing operations of the touch sensors during a touch period based on changes in an amount of surface charge of the transparent conductive layer depending on whether or not the polarizing plate is touched.

This application is a Divisional of Copending U.S. patent applicationSer. No. 12/318,422, filed Dec. 29, 2008 and claims the benefit ofKorean Patent Application No. 10-2008-0059896 filed on Jun. 24, 2008,both of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

2. Field of the Invention

The present invention relates to an in-cell touch panel type liquidcrystal display, and more specifically to a liquid crystal displaycapable of accurately sensing whether or not a liquid crystal displaypanel is touch.

2. Background of the Related Art

A liquid crystal display (LCD) displays an image by controlling lighttransmitted through a liquid crystal layer using an electric fieldgenerated in response to a video signal and applied to the liquidcrystal layer. Because the liquid crystal display is a thin, small-sizedflat panel display device with low power consumption, the liquid crystaldisplay has been used in personal computers such as notebook PCs, officeautomation equipment, audio/video equipment, and the like. Inparticular, because an active matrix type liquid crystal displayincludes a switching element in each liquid crystal cell that isactively controlled, the active matrix type liquid crystal display isadvantageous in displaying a moving picture. A thin film transistor(TFT) has been mainly used as the switching element of the active matrixtype liquid crystal display.

In general, an active matrix type liquid crystal display convertsdigital video data into an analog data voltage based on a gammareference voltage. As shown in FIG. 1, the analog data voltage is thenapplied to a data line DL while a scan pulse is applied to a gate lineGL. The scan pulse activates a thin film transistor TFT connectedthereto, thereby charging a liquid crystal cell Clc with the datavoltage on the data line DL. The thin film transistor TFT includes agate electrode connected to the gate line GL, a source connected to thedata line DL, and a drain electrode commonly connected to a pixelelectrode of the liquid crystal cell Clc and one electrode of a storagecapacitor Cst. A common voltage Vcom is applied to a common electrode ofthe liquid crystal cell Clc. When the scan pulse is applied to the gateline GL, the thin film transistor TFT is turned on, and a channel isformed between the source and drain electrodes of the thin filmtransistor TFT. Hence, a voltage on the data line DL is supplied to thepixel electrode of the liquid crystal cell Clc. Additionally, when thethin film transistor TFT is turned on, the storage capacitor Cst ischarged with the data voltage applied through the data line DL, therebykeeping the voltage level of the liquid crystal cell Clc constant. Theorientation of liquid crystal molecules in the liquid crystal cell Clcchanges due to an electric field generated between the pixel electrodeand the common electrode, thereby changing the incident light. Becausethe liquid crystal display is generally a light receiving element (i.e.,liquid crystals do not generate light), the liquid crystal displayadjusts luminance of the screen using light produced by a backlight unitformed in the rear of a liquid crystal display panel.

Recently, a touch screen panel attached to the liquid crystal displayhas been proposed. The touch screen panel generally attached on theliquid crystal display is a user interface that detects changes inelectrical characteristics at a touch position where an opaque object,such as a finger or a pen, contacts the touch screen panel. When auser's finger or a touch pen contacts the screen of the touch screenpanel of the liquid crystal display, a display device detects theinformation of the touch position and uses the information for variousapplications.

However, the touch screen panel of the liquid crystal display generallyincreases the manufacturing cost of the liquid crystal display, mayreduce the manufacturing yield due to the added process of attaching thetouch screen panel to the liquid crystal display, may reduce brightnessof the liquid crystal display, increases the thickness of the liquidcrystal display, and the like.

To solve the above-described problems, rather than attaching a touchscreen panel, an in-cell touch panel type liquid crystal display hasbeen proposed. An in-cell touch panel type liquid crystal displayincludes a touch sensor circuit including a sensor thin film transistor(TFT) formed inside the liquid crystal cell Clc of the liquid crystaldisplay. As shown in FIG. 2, the touch sensor circuit includes a sensorTFT that changes a light current “i” depending on changes in the amountof external light coming into the panel, a sensor capacitor Cst2 thatstores a charge generated by the light current “i,” and a switching TFTthat switches on and off an output of the charge stored in the sensorcapacitor Cst2. A bias voltage Vbias is supplied to a gate electrode ofthe sensor TFT and is set at a voltage level equal to or smaller than athreshold voltage of the gate electrode of the sensor TFT.

In the touch sensor circuit shown in FIG. 2, the light current (i) of asensor TFT in a touch area is larger than the light current of a sensorTFT in a non-touch area when the outside environment is darker than thebacklight (e.g., indoors). On the other hand, the light current (i) of asensor TFT in a touch area is smaller than the light current of a sensorTFT in a non-touch area when the outside environment is brighter thanthe backlight (e.g., outdoors). In either circumstance, a light sensingsignal produced in the touch area is different than a light sensingsignal in the non-touch area. Accordingly, the liquid crystal displaydetects the touch position information based on the light sensingsignals of the touch sensor circuit.

Because the related art in-cell touch panel type liquid crystal displaydetects the touch position based on only a relative difference betweenthe light currents flowing in the sensor TFTs, detection of whether ornot the liquid crystal display panel is actually touched cannot bedetermined accurately. For example, FIG. 3A shows that if the user'sfingers approach the liquid crystal display without touching the liquidcrystal display in a strong illuminance environment (e.g., outdoorenvironment), the related art in-cell touch panel type liquid crystaldisplay may not be able distinguish from an actual touch condition shownin FIG. 3B. This reduces the sensing accuracy, thereby causing amaloperation of the liquid crystal display.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a liquid crystaldisplay with improved sensing accuracy.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a liquidcrystal display comprises a liquid crystal display panel including apixel array that displays an image and touch sensors that sense a touchposition depending on an amount of receiving light, a transparentconductive layer on one substrate of the liquid crystal display paneltransmitting display light, a portion of the transparent conductivelayer being connected to a ground level voltage source, a polarizingplate on the transparent conductive layer, a driving voltage supplycircuit to generate a driving voltage required to perform light sensingoperations of the touch sensors during a touch period based on changesin an amount of surface charge of the transparent conductive layerdepending on whether or not the polarizing plate is touched, and asignal transmitting unit to electrically connect the transparentconductive layer to the driving voltage supply circuit.

When a user touches the polarizing plate with his or her finger, thepolarizing plate serves as a dielectric to form an equivalent capacitorbetween the user's finger and the transparent conductive layer. Theamount of surface charge of the transparent conductive layer has adifferent value during touch and non-touch operations.

The polarizing plate includes a conductive layer and a dielectric layerbetween the conductive layer and the one substrate of the liquid crystaldisplay panel. When a user touches the polarizing plate with his or herfinger, the dielectric layer serves as a dielectric to form anequivalent capacitor between the conductive layer and the transparentconductive layer. The amount of surface charge of the transparentconductive layer has a different value during touch and non-touchoperations.

The signal transmitting unit includes a touch output pad on anothersubstrate of the liquid crystal display panel, a conductive tape toelectrically connect the transparent conductive layer to one surface ofthe touch output pad, a printed circuit board on which the drivingvoltage supply circuit is mounted, and a flexible wiring film toelectrically connect another surface of the touch output pad to theprinted circuit board.

The signal transmitting unit includes a printed circuit board on whichthe driving voltage supply circuit is mounted, and a flexible wiringfilm to electrically connect the transparent conductive layer to theprinted circuit board.

In another aspect, a liquid crystal display comprises a liquid crystaldisplay panel including a pixel array that displays an image and touchsensors that sense a touch position depending on an amount of receivinglight, a first transparent conductive layer on one substrate of theliquid crystal display panel transmitting display light, the transparentconductive layer being connected to a ground level voltage source, apolarizing plate on the first transparent conductive layer, a secondtransparent conductive layer that is formed on the polarizing plate tobe exposed to the outside, the first and second transparent conductivelayers being on opposite sides of the polarizing plate, a drivingvoltage supply circuit to generate a driving voltage required to performlight sensing operations of the touch sensors during a touch periodbased on changes in an amount of surface charge of the secondtransparent conductive layer depending on whether or not the secondtransparent conductive layer is touched, and a signal transmitting unitto electrically connect the second transparent conductive layer to thedriving voltage supply circuit.

When a user touches the second transparent conductive layer with his orher finger, the polarizing plate serves as a dielectric to form anequivalent capacitor between the first and second transparent conductivelayers. The amount of surface charge of the second transparentconductive layer has a different value during touch and non-touchoperations.

In still another aspect, a liquid crystal display comprises a liquidcrystal display panel including a pixel array that displays an image andtouch sensors that sense a touch position depending on an amount ofreceiving light, a polarizing plate on one substrate of the liquidcrystal display panel transmitting display light, the polarizing plateincluding a conductive layer, a driving voltage supply circuit togenerate a driving voltage required to perform light sensing operationsof the touch sensors during a touch period based on changes in an amountof surface charge of the conductive layer depending on whether or notthe polarizing plate is touched, and a signal transmitting unit toelectrically connect the conductive layer to the driving voltage supplycircuit.

When a user touches the polarizing plate with his or her finger, adielectric layer on the conductive layer serves as a dielectric to forman equivalent capacitor between the user's finger and the conductivelayer. The amount of surface charge of the conductive layer has adifferent value during touch and non-touch operations.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is an equivalent circuit diagram of an active matrix type liquidcrystal display;

FIG. 2 is a diagram for explaining an operation of a touch sensorcircuit;

FIGS. 3A and 3B are diagrams showing when a liquid crystal display panelwas not touched and was touched, respectively;

FIG. 4 is a block diagram of a liquid crystal display according to anexemplary embodiment of the invention;

FIG. 5 illustrates a first exemplary method for forming an equivalentcapacitor;

FIG. 6 illustrates a second exemplary method for forming an equivalentcapacitor;

FIG. 7 illustrates a third exemplary method for forming an equivalentcapacitor;

FIG. 8 illustrates a first exemplary method for removing a noise;

FIG. 9 illustrates a second exemplary method for removing a noise;

FIG. 10 illustrates a first exemplary configuration of a signaltransmitting unit;

FIG. 11 illustrates a second exemplary configuration of a signaltransmitting unit;

FIG. 12 illustrates an exemplary configuration of a sensing circuitshown in FIG. 4;

FIG. 13 illustrates an exemplary configuration of a driving voltagesupply circuit shown in FIG. 4;

FIG. 14 is an equivalent circuit diagram of a pixel shown in FIG. 4;

FIG. 15 illustrates an exemplary connection structure between touchsensor circuits; and

FIG. 16 is an exemplary waveform diagram of driving voltages applied tothe touch sensor circuits of FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail embodiments of the inventionexamples of which are illustrated in the accompanying drawings.

FIG. 4 is a block diagram of a liquid crystal display according to anexemplary embodiment of the invention. As shown in FIG. 4, the liquidcrystal display according to the exemplary embodiment of the inventionincludes a liquid crystal display panel 10, a data drive circuit 20, agate drive circuit 30, a timing controller 40, a sensing circuit 50, adriving voltage supply circuit 60, a backlight unit 70, and a readoutintegrated circuit (IC) 80. The liquid crystal display panel 10 includesa plurality of gate lines G0 to Gn, a plurality of data lines D1 to Dm,a plurality of driving voltage supply lines VL1 to VLn, and a pixel Phaving a touch sensor circuit at each crossing of the lines G0 to Gn, D1to Dm, and VL1 to VLn.

The data drive circuit 20 supplies a data voltage to the data lines D1to Dm, and the gate drive circuit 30 supplies a scan pulse to the gatelines G0 to Gn. The timing controller 40 controls drive timing of thedata drive circuit 20 and the gate drive circuit 30. The sensing circuit50 senses whether or not a user touches the liquid crystal display panel10 with his or her finger and generates a touch/non-touch sensing signalTS. The driving voltage supply circuit 60 changes the level of a drivingvoltage required to drive the touch sensor circuit inside the pixel Pdepending on the touch/non-touch sensing signal TS and supplies thechanged driving voltages to the driving voltage supply lines VL1 to VLn.The backlight unit 70 is positioned in the rear of the liquid crystaldisplay panel 10 and produces light. The readout IC 80 is commonlyconnected to readout lines ROL1 to ROLm of the liquid crystal displaypanel 10.

The liquid crystal display panel 10 includes an upper substrateincluding a color filter, a lower substrate on which a pixel circuit andthe pixels P are formed, and a liquid crystal layer interposed betweenthe upper substrate and the lower substrate. The data lines D1 to Dmcross the gate lines G0 to Gn on the lower substrate of the liquidcrystal display panel 10. The driving voltage supply lines VL1 to VLnare parallel to the gate lines G0 to Gn and formed on the lowersubstrate of the liquid crystal display panel 10. The readout lines ROL1to ROLm are perpendicular to the gate lines G0 to Gn. As shown in FIG.14, a pixel circuit P1 is formed at each region where the data lines D1to Dm and the gate lines G0 to Gn cross, and a touch sensor circuit P2is formed in a region where the driving voltage supply lines VL1 to VLnand the readout lines ROL1 to ROLm cross. The driving voltage supplylines VL1 to VLn each include first supply lines VL1 a to VLna forsupplying a driving voltage to the touch sensor circuit P2 and secondsupply lines VL1 b to VLnb for supplying a bias voltage to the touchsensor circuit P2. The touch sensor circuit P2 generates thetouch/non-touch sensing signal TS depending on the touch or non-touchoperation and supplies the touch/non-touch sensing signal TS to thereadout IC 80 through the readout lines ROL1 to ROLm.

A black matrix is formed on the upper substrate of the liquid crystaldisplay panel 10 to cover an interface between the pixels P. A commonelectrode and a pixel electrode are on opposite sides of the liquidcrystal layer. The common electrode receiving a common voltage is formedon the upper substrate of the liquid crystal display panel 10 in avertical electric mode such as a twisted nematic (TN) mode and avertical alignment (VA) mode. In a transverse electric mode such as anin-plane switching (IPS) mode and a fringe field switching (FFS) mode,the common electrode is formed on the lower substrate of the liquidcrystal display panel 10.

The data drive circuit 20 converts digital video data RGB into an analoggamma compensation voltage based on a gamma reference voltage generatedby a gamma reference voltage generation unit (not shown) in response toa data control signal DDC produced by the timing controller 40. Theanalog gamma compensation voltage serving as a data voltage is suppliedto the liquid crystal display panel 10. The gate drive circuit 30generates scan pulses in response to a gate control signal GDC producedby the timing controller 40 and sequentially supplies the scan pulses tothe gate lines G1 to Gn to select horizontal lines of the liquid crystaldisplay panel 10 to which the data voltage is supplied.

The timing controller 40 rearranges the digital video data RGB receivedfrom a system 90 in conformity with the liquid crystal display panel 10and supplies the digital video data RGB to the liquid crystal displaypanel 10. The timing controller 40 produces the data control signal DDCfor controlling the data drive circuit 20, the gate control signal GDCfor controlling the gate drive circuit 30, and a readout control signalRDC for controlling the readout IC 80 using timing control signalsVsync, Hsync, DCLK, and DE received from the system 90.

The backlight unit 70 is positioned in the rear of the liquid crystaldisplay panel 10 and includes a plurality of lamps installed to overlapthe liquid crystal display panel 10. The lamp of the backlight unit 70may include a cold cathode fluorescent lamp (CCFL), an externalelectrode fluorescent lamp (EEFL), and a heat cathode fluorescent lamp(HCFL). The lamps provide light at the rear of the liquid crystaldisplay panel 10 and driven by an inverter (not shown). The backlightunit 70 may include a plurality of light emitting diodes instead of thelamps or may include both the lamps and the light emitting diodes.

As shown in FIG. 5, upper and lower polarizing plates 14 and 16 forselecting linear polarization are formed on the upper and lowersubstrates of the liquid crystal display panel 10, respectively. Each ofthe upper and lower polarizing plates 14 and 16 are generally formed ofa plurality of organic material layers including polyvinyl alcohol (PVA)being a high polymer polarization medium layer for polarizing incidentlight. When the user touches the upper polarizing plate 14 with his/herfinger, all or some of the organic material layers of the upperpolarizing plate 14 are positioned between the user's finger and atransparent conductive layer 12 serving as electrodes to serve as adielectric of an equivalent capacitor. Hence, the amount of the surfacecharge Q1 of the transparent conductive layer 12 when the upperpolarizing plate 14 is touched is different from the amount of thesurface charge Q2 of the transparent conductive layer 12 when the upperpolarizing plate 14 is not touched due to the capacitive effect of theequivalent capacitor formed by the user's finger. Changes in the amountof surface charge Q during the touch and non-touch operations aresupplied to the sensing circuit 50 through a signal transmitting unit 18to detect whether or not the liquid crystal display panel 10 is touched.As above, the equivalent capacitor is used to extract the changes in theamount of surface charge Q during the touch and non-touch operations,and there are several methods for forming the equivalent capacitor.

As a first exemplary method for forming an equivalent capacitor, asshown in FIG. 5, the transparent conductive layer 12 formed of amaterial such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO) isformed between the upper polarizing plate 14 transmitting display lightand the upper substrate of the liquid crystal display panel 10. When theuser touches the upper polarizing plate 14 with his/her finger, theuser's finger and the transparent conductive layer 12 serve aselectrodes of an equivalent capacitor C1 and the upper polarizing plate14 serves as a dielectric of the equivalent capacitor C1. The upperpolarizing plate 14 includes the plurality of organic material layerssuch as a polyvinyl alcohol (PVA) layer for polarizing incident layer, atri-acetyl-cellulose (TAC) layer for protecting the PVA layer, ananti-glaring (AG) layer for glare prevention, and an adhesive layer usedto attach the upper polarizing plate 14 to the transparent conductivelayer 12. The upper polarizing plate 14 shown in FIG. 5 may be replacedwith a conductive polarizing plate 24 shown in FIG. 6.

As a second exemplary method for forming an equivalent capacitor, asshown in FIG. 6, the conductive polarizing plate 24 further includes aconductive layer AS between an adhesive layer and a TAC layer. Theconductive layer AS and the transparent conductive layer 12 serving aselectrodes are on opposite sides of the adhesive layer serving as adielectric to form an equivalent capacitor C2. The signal transmittingunit 18 is connected to the transparent conductive layer 12 to supplychanges in the amount of surface charge Q of the transparent conductivelayer 12 during touch and non-touch operations to the sensing circuit50.

As a third exemplary method for forming an equivalent capacitor, asshown in FIG. 7, only a conductive upper polarizing plate 34 may be usedto form an equivalent capacitor without the transparent conductivelayer. The conductive polarizing plate 34 further includes a conductivelayer AS between an adhesive layer and a TAC layer. The user's fingerand the conductive layer AS serving as electrodes are on opposite sidesof a plurality of organic material layers such as an AG layer, a TAClayer, and a PVA layer serving as a dielectric to form an equivalentcapacitor C3. The signal transmitting unit 18 is connected to theconductive layer AS to supply changes in the amount of surface charge Qof the conductive layer AS during touch and non-touch operations to thesensing circuit 50.

As a first exemplary method for removing a noise, as shown in FIG. 8,the transparent conductive layer 12 may include ground patterns A1connected to a ground level voltage source GND and sensing conductivepatterns A2 between the ground patterns A1, so as to remove a noiseincluded in the changes in the amount of surface charge Q of thetransparent conductive layer 12. As above, when the transparentconductive layer 12 includes the ground patterns A1, a noise caused bythe common electrode is removed in the vertical electric mode in whichthe common electrode is formed on the upper substrate of the liquidcrystal display panel 10. Hence, the sensing accuracy can be greatlyimproved.

As a second exemplary for removing a noise, as shown in FIG. 9, an uppertransparent conductive layer 12 b is formed on the upper polarizingplate 14 to be connected to the ground level voltage source GND. A lowertransparent conductive layer 12 a is opposite to the upper transparentconductive layer 12 b with the upper polarizing plate 14 therebetween.The transparent conductive layers 12 a and 12 b serving as electrodesare on opposite sides of the upper polarizing plate 14 serving as adielectric to form an equivalent capacitor C4. The signal transmittingunit 18 is connected to the upper transparent conductive layer 12 b tosupply changes in the amount of surface charge Q of the uppertransparent conductive layer 12 b during touch and non-touch operationsto the sensing circuit 50.

As shown in FIG. 10, the signal transmitting unit 18 includes aconductive tape 18 a, a touch output pad 18 b, and a flexible wiringfilm 18 c. FIG. 10 shows that the conductive tape 18 a electricallyconnects the transparent conductive layer 12 shown in FIGS. 5 and 6 toone surface of the touch output pad 18 b. Although it is not shown, theconductive tape 18 a electrically connects the conductive layer AS shownin FIG. 7 to one surface of the touch output pad 18 b and electricallyconnects the transparent conductive layer 12 b shown in FIG. 9 to onesurface of the touch output pad 18 b. The touch output pad 18 b isformed on the lower substrate of the liquid crystal display panel 10using a line-on-glass method. The touch output pad 18 b includes a gatemetal layer or a source-drain metal layer. The touch output pad 18 b andgate pads or data pads of the lower substrate of the liquid crystaldisplay panel 10 are formed on the lower substrate of the liquid crystaldisplay panel 10. The flexible wiring film 18 c includes a flexibleprinted circuit (FPC) and electrically connects the other surface of thetouch output pad 18 b to a printed circuit board (PCB). The data drivecircuit 20, the gate drive circuit 30, the timing controller 40, thesensing circuit 50, and the driving voltage supply circuit 60 aremounted on the printed circuit board.

FIG. 11 shows the signal transmitting unit 18 that includes a flexiblewiring film 18 in addition to a FPC. The flexible wiring film 18directly connects the transparent conductive layer 12 to the PCB.

FIG. 12 illustrates an exemplary configuration of the sensing circuit 50that includes a charge amount sensing unit 52, a QV converting unit 54,an AD converting unit 56, and a touch or non-touch sensing signalgeneration unit 58. The sensing circuit 50 senses the changes in theamount of surface charge and generates a touch or non-touch sensingsignal.

The charge amount sensing unit 52 is connected to the signaltransmitting unit 18 and senses the amount of surface charge Q of thetransparent conductive layer 12 or 12 b or the conductive layer AS ofthe polarizing layer. As an example, the amount of surface charge Q ofthe transparent conductive layer 12 is sensed. As described above, theamount of surface charge Q of the transparent conductive layer 12 has adifferent value during the touch and non-touch operations. For example,the amount of surface charge Q of the transparent conductive layer 12during the touch operation has a first charge amount Q1, and the amountof surface charge Q of the transparent conductive layer 12 during thenon-touch operation has a second charge amount Q2.

The QV converting unit 54 converts the amount of surface charge Q (i.e.,the first charge amount Q1 or the second charge amount Q2) received fromthe charge amount sensing unit 52 into an analog voltage value. The ADconverting unit 56 converts the analog voltage value received from theQV converting unit 54 into a digital voltage value.

The touch or non-touch sensing signal generation unit 58 produces thetouch/non-touch sensing signal TS based on the digital voltage valuereceived from the AD converting unit 56. The touch/non-touch sensingsignal TS is generated as a touch signal when the digital voltage valueof the first charge amount Q1 is present, and the touch/non-touchsensing signal TS is generated as a non-touch signal when the digitalvoltage value of the second charge amount Q2 is present. Thetouch/non-touch sensing signal TS is a transistor-to-transistor logic(TTL) signal swing between 0 V and 3.3 V.

FIG. 13 illustrates an exemplary driving voltage supply circuit 60 thatincludes a level shifter 62. The level shifter 62 level-shifts the TTLlevel of the touch/non-touch sensing signal TS into a driving voltagelevel sufficient to drive the touch sensor circuit P2 inside the pixel P(FIG. 8). As a result of the level shifting operation, the drivingvoltage supply circuit 60 generates a driving voltage Vdry swing betweena high potential Vh and a low potential V1 to supply the driving voltageVdry to the first supply lines VL1 a to VLna of the driving voltagesupply lines VL1 to VLn. The touch sensor circuit P2 performs a lightsensing operation when the driving voltage Vdry of the high potential Vhis generated in response to the touch signal. The touch sensor circuitP2 stops the light sensing operation when the driving voltage Vdry ofthe low potential V1 is generated in response to the non-touch signal.Although it is not shown, the driving voltage supply circuit 60generates a bias voltage to supply the bias voltage to the second supplylines VL1 b to VLnb of the driving voltage supply lines VL1 to VLn.

The readout IC 80 includes a plurality of circuits respectivelyconnected to the readout lines ROL1 to ROLm of the liquid crystaldisplay panel 10. The readout IC 80 converts a light sensing signalreceived from the readout lines ROL1 to ROLm into a digital signal to besupplied to the system 90. The system 90 performs a touch recognitionprocess and a coordinate calculation process through a touch algorithm,and indicates the area of touch on the liquid crystal display panel 10.

FIG. 14 illustrates an equivalent circuit diagram of the pixel P brieflydescribed above. As shown in FIG. 14, the pixel P includes a pixelcircuit P1 at a crossing region of the j-th gate line Gj and the j-thdata line Dj, and a touch sensor circuit P2 at a crossing region of thej-th first supply line VLja, the j-th second supply line VLjb, and thej-th readout line ROLj. The pixel circuit P1 includes liquid crystalcells Clc, a pixel thin film transistor (TFT) TFT 1 for driving theliquid crystal cells Clc at a crossing region of the j-th gate line Gjand the j-th data line Dj, and a storage capacitor Cst1 that keeps acharging voltage of the liquid crystal cells Clc constant during oneframe.

The pixel TFT TFT1 supplies the data voltage supplied through the j-thdata line Dj to the pixel electrode of the liquid crystal cell Clc inresponse to the scan pulse received through the j-th gate line Gj. Forthis, the pixel TFT TFT1 includes a gate electrode connected to the j-thgate line Gj, a source electrode connected to the j-th data line Dj, anda drain electrode connected to the pixel electrode of the liquid crystalcell Clc. The liquid crystal cell Clc is charged with a voltagemagnitude corresponding to a difference between the data voltage and thecommon voltage Vcom. The arrangement of liquid crystal molecules changesby an electric field formed by the voltage magnitude, and thus theamount of transmitted light may be controlled.

The touch sensor circuit P2 includes a sensor TFT S-TFT, a sensorcapacitor Cst2, and a switch TFT TFT2. The sensor TFT S-TFT generates alight current “i” when the driving voltage Vdry has a high potential Vhand does not generate the light current “i” when the driving voltageVdry has a low potential Vl. The sensor capacitor Cst2 stores chargesgenerated by the light current “i.” The switch TFT TFT2 switches thecharges stored in the sensor capacitor Cst2 to the readout line ROLj.

The sensor TFT S-TFT includes a gate electrode connected to the secondsupply line VLjb, a source electrode connected to the first supply lineVLja, and a drain electrode connected to a first node N1. A bias voltageVbias set at a voltage equal to or smaller than a threshold voltage ofthe gate electrode of the sensor TFT S-TFT is supplied to the gateelectrode of the sensor TFT S-TFT. The driving voltage Vdry swingbetween the high potential Vh and the low potential Vl is supplied tothe source electrode of the sensor TFT S-TFT depending on whether or notthe upper polarizing plate 14 is touched. The sensor TFT S-TFT performsa light sensing operation during when the driving voltage Vdry ismaintained at the high potential Vh in response to the touch operation,thereby increasing the accuracy of sensing operation. On the other hand,the sensor TFT S-TFT stops the light sensing operation during when thedriving voltage Vdry is maintained at the low potential Vl in responseto the non-touch operation. Accordingly, degradation of the sensor TFTS-TFT that may be caused by continuous light sensing operation isavoided.

The sensor TFT S-TFT is not covered by the black matrix of the uppersubstrate unlike the pixel TFT TFT1 and the switch TFT2. Therefore, thesensor TFT S-TFT generates the light current “i” in response to thelight coming from the outside when the driving voltage Vdry ismaintained at the high potential Vh. Furthermore, the amount of lightcurrent “i” generated by the sensor TFT S-TFT depends on whether or notthe sensor TFT S-TFT corresponds to a touch position. For example, in anenvironment that is darker than the backlight (e.g., indoors), thesensor TFT S-TFT in a touch position generates a larger light current“i” than the sensor TFT S-TFT in a non-touch position. On the otherhand, in an environment that is brighter than the backlight (e.g.,outdoors), the sensor TFT S-TFT in a touch position generates a smallerlight current “i” than the sensor TFT S-TFT in a non-touch position.

The sensor capacitor Cst2 connected between the first node N1 and thesecond supply line VLjb stores the charges generated by the lightcurrent “i.” A voltage VN1 at the first node N1 gradually increases bythe charges stored in the sensor capacitor Cst2 until the switch TFTTFT2 is turned on. The voltage VN1 at the first node N1 changesdepending on whether or not the sensor TFT S-TFT is in a touch positionwhen the driving voltage Vdry is at the high potential Vh. For example,in an environment that is darker than the backlight (e.g., indoors), thevoltage VN1 at the first node N1 is higher when the sensor TFT S-TFT isin a touch position than when the sensor TFT S-TFT is in a non-touchposition. On the other hand, in an environment that is brighter than thebacklight (e.g., outdoors), the voltage VN1 at the first node N1 lowerwhen the sensor TFT S-TFT is in the touch position than when the sensorTFT S-TFT is not in the touch position. The voltage VN1 at the firstnode N1 is held at an initial value during when the driving voltage Vdryis maintained at the low potential Vl.

The switch TFT TFT2 includes a gate electrode connected to the (j-1)-thgate line Gj-1, a source electrode connected to the first node N1, and adrain electrode connected to the j-th readout line ROLj. The switch TFTTFT2 is turned on in response to the scan pulse SPj-1 supplied to the(j-1)-th gate line Gj-1 and thus outputs the voltage VN1 at the firstnode N1 as a light sensing signal to the j-th readout line ROLj.

FIG. 15 illustrates a first exemplary connection structure between thetouch sensor circuits P2. FIG. 16 is an exemplary waveform diagram ofthe driving voltage Vdry applied to the touch sensor circuits P2 of FIG.15.

As shown in FIGS. 15 and 16, the touch sensor circuits P2 are commonlyconnected to each of the first supply lines VL1 a to VLna. Further, thefirst supply lines VL1 a to VLna are commonly connected to receive thedriving voltage Vdry generated by the driving voltage supply circuit 60.In the present embodiment, the driving voltage Vdry is at a highpotential Vh during the on-time of the touch/non-touch sensing signalTS, and the driving voltage Vdry is at a low potential Vl during theoff-time of the touch/non-touch sensing signal TS. The liquid crystaldisplay according to the exemplary embodiment of the invention generatesthe driving voltage Vdry at the high potential Vh during only theon-time of the touch/non-touch sensing signal TS, and intermittentlydrives the touch sensor circuits P2 based on the driving voltage Vdry ofthe high potential Vh. Accordingly, the accuracy of sensing operationcan be greatly improved as compared with the related art, and thedegradation of the sensor TFTs S-TFT inside the touch sensor circuits P2can be greatly reduced as compared with the related art.

As described above, the liquid crystal display according to theexemplary embodiments of the invention accurately senses whether or notthe user touches the liquid crystal display panel with his/her finger bydetecting the changes in the amount of surface charge of the transparentconductive layer or the conductive layer inside the polarizing plateduring the touch and non-touch operations, thereby greatly increasingthe accuracy of sensing operation.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the embodiments of theinvention without departing from the spirit or scope of the invention.Thus, it is intended that embodiments of the invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

1. A liquid crystal display comprising: a liquid crystal display panelincluding a pixel array that displays an image and touch sensors thatsense a touch position depending on an amount of receiving light; afirst transparent conductive layer on one substrate of the liquidcrystal display panel transmitting display light, the transparentconductive layer being connected to a ground level voltage source; apolarizing plate on the first transparent conductive layer; a secondtransparent conductive layer that is formed on the polarizing plate tobe exposed to the outside, the first and second transparent conductivelayers being on opposite sides of the polarizing plate; a drivingvoltage supply circuit to generate a driving voltage required to performlight sensing operations of the touch sensors during a touch periodbased on changes in an amount of surface charge of the secondtransparent conductive layer depending on whether or not the secondtransparent conductive layer is touched; and a signal transmitting unitto electrically connect the second transparent conductive layer to thedriving voltage supply circuit.
 2. The liquid crystal display of claim1, wherein when a user touches the second transparent conductive layerwith his or her finger, the polarizing plate serves as a dielectric toform an equivalent capacitor between the first and second transparentconductive layers, wherein the amount of surface charge of the secondtransparent conductive layer has a different value during touch andnon-touch operations.
 3. The liquid crystal display of claim 1, whereinthe signal transmitting unit includes: a touch output pad on anothersubstrate of the liquid crystal display panel; a conductive tape toelectrically connect the second transparent conductive layer to onesurface of the touch output pad; a printed circuit board on which thedriving voltage supply circuit is mounted; and a flexible wiring film toelectrically connect another surface of the touch output pad to theprinted circuit board.
 4. The liquid crystal display of claim 1, whereinthe signal transmitting unit includes: a printed circuit board on whichthe driving voltage supply circuit is mounted; and a flexible wiringfilm to electrically connect the second transparent conductive layer tothe printed circuit board.